Don't Get Used to the Idea of a Global Warming 'Slowdown'

One of the puzzling things about climate change is a recent slowdown in warming (or as some exaggerators refer to it, a "pause"). The planet's temperatures ticked up by 0.22 degrees Fahrenheit each decade after 1951. But beginning in 1998, the rate slowed to 0.09 degrees per decade, despite the world's nations still pouring copious greenhouse gases into the atmosphere.

There are many theories to explain this reduced rate of warming (see below), yet climate-change skeptics have used this event to compose a rousing symphony of pishes and humbugs. For instance, Texas Senator Ted Cruz recently told CNN "there has been no recorded warming" in the past 15 years, and that the "data are not supporting what the advocates are arguing." And the failure of climate models to accurately predict the slowdown was hiding in plain sight in a February editorial in the Wall Street Journal, penned by two atmospheric scientists from the University of Alabama in Huntsville. "We might forgive these modelers if their forecasts had not been so consistently and spectacularly wrong," they wrote, claiming that the "forecasts for future temperatures have continued to be too warm."

But "too warm" is a concept we need to wrap our soon-to-be-baked brains around, according to new research from NASA's Drew Shindell. After performing a region-specific analysis of the things that affect the global climate, Shindell has come to the conclusion that, slowdown be damned, we are still looking at a vast leap in the earth's heat levels. In fact, there could be a warming increase about 20 percent greater than indicated by surface-temperature observations from the last 150 years, according to his new study in Nature Climate Change.

The above map of the globe, furnished by NASA's visualization and simulation teams, shows where the heat is likely to come down hard by 2099. Dark-red areas at the North Pole indicate positive temperature anomalies of up to 25 degrees. Much of Canada could see hikes of 10 to 20 degrees and in the United States, 5 to 12.5 degrees. That would mean that future warming will be much worse than described in the latest report from the Intergovernmental Panel on Climate Change (which took the slowdown into account when making its projections). NASA has the figures:

To put a number to climate change, researchers calculate what is called Earth's "transient climate response." This calculation determines how much global temperatures will change as atmospheric carbon dioxide continues to increase – at about 1 percent per year – until the total amount of atmospheric carbon dioxide has doubled. The estimates for transient climate response range from near 2.52 F (1.4 C) offered by recent research, to the IPCC's estimate of 1.8 F (1.0 C). Shindell's study estimates a transient climate response of 3.06 F (1.7 C), and determined it is unlikely values will be below 2.34 F (1.3 C).

So how did Shindell reach this grim outcome? Partly by taking an exacting approach to atmospheric aerosols, which are natural and human-generated particles that play a role in the distribution of solar energy. Previous modeling runs had assumed they were scattered evenly around the globe. But aerosols are actually more prevalent in the Northern Hemisphere due to heavier industrialization and larger landmasses. Shindell took this inequality into account to make his harsher prediction. "I wish it weren't so," he says, "but forewarned is forearmed."

For those wondering why global warming has been slower these past years, scientists have posed a number of possible reasons. One is that the ocean is sucking up some of the excess heat, as the atmosphere can only hold so much at any given time. One NASA oceanographer told Scientific American that the world's seas, not surface temperatures, should be the current barometer of climate change because their temperatures are going up "like gangbusters." Other suspects include several recent sky-dimming volcanic eruptions and an abnormal pattern of trade winds in the Pacific.

Whatever's putting on the brakes, the national science academies of the U.S. and U.K. warn in a February report not to expect it to last. Although there might be "slowdowns and accelerations in warming lasting a decade or more," they write, the clear long-term trend is "substantial increases in global average surface temperature and important changes in regional climate."